Hierarchical HCF@NC/Co Derived from Hollow Loofah Fiber Anchored with Metal–Organic Frameworks for Highly Efficient Microwave Absorption

Hierarchical electromagnetic wave (EMW) absorption materials with a dielectric-magnetic dual-loss mechanism are promising candidates for highly efficient EMW attenuation. Herein, hierarchical dielectric-magnetic composite hollow carbon fiber@nitrogen-doped carbon/Co (HCF@NC/Co) was successfully synthesized via in situ growth of two-dimensional (2D) Co metal-organic framework (MOF) (ZIF-67) nanosheets on the surface of hollow loofah fiber (HLF), followed by a calcination process, where the aggregation of carbonized MOFs was effectively avoided to construct a homogeneous hierarchical one-dimensional structure. Based on the advantages of the carbon/Co dielectric-magnetic dual-loss mechanism that results in good impedance matching and multiple polarization loss arising from the extensive heterointerfaces (e.g., HCF-NC/Co, air-carbon, nitrogen-carbon, and Co-carbon interfaces), dipole active sites (e.g., doped N, Co particle, and crystalline defects in graphitic carbon), and hierarchical porous structures, optimal EMW absorption performance of HCF@NC/Co is achieved through regulating the calcination temperature and filler content, where the HCF@NC/Co calcinated at 700 °C exhibits a minimum reflection loss (RL_min) value of -50.14 dB with only 14% filler loading and 2.25 mm thickness, and the maximum effective absorption bandwidth (EAB_max) also reaches 7.36 GHz. Meanwhile, adjustable EAB can also be achieved by optimizing the sample thickness, making it applicable in a wider frequency region. It is expected that our prepared HCF@NC/Co might shed light on designing lightweight and highly efficient EMW MOF-derived EMW absorbing materials.